1. Field
Apparatuses and methods consistent with exemplary embodiments relate to a wireless personal area network (WPAN), and more particularly, to transceiving data between devices in the WPAN using directional beams.
2. Description of the Related Art
A wireless personal area network (WPAN) is a wireless network in which devices arranged at short distances from one another transceive data at low power. In a WPAN, data communication is performed using a time division multiple access (TDMA) method. Accordingly, devices desiring to perform data communication occupy a channel exclusively for a channel time allocation period (CTAP), which is allocated by a device referred to as a Piconet coordinator (PNC), to perform data communication. Further description on WPAN is disclosed in IEEE 802.15 family standard documents, and will therefore be omitted here.
Recently, studies on a high speed data transmission technology using a millimeter (mm)-wave, which is a high frequency wave having a short wavelength of 1-10 mm and high directivity, are ongoing. For example, an IEEE 802.15.3c Task Group is working on standardization of a physical layer (PHY) for data communication using an mm-wave in a WPAN. As described above, mm-wave is a high frequency wave having a short wavelength of 1-10 mm and high directivity, and can be used for transmission of large capacities of data (such as high definition (HD) quality moving images) in a home network.
FIG. 1 is a schematic view for comparing frequency bands used in data communication according to IEEE 802.11 family standards and in communication using an mm-wave.
As illustrated in FIG. 1, the carrier frequency of IEEE 802.11b standard or IEEE 802.11 g standard is 2.4 GHz and the channel bandwidth thereof is about 20 MHz. Also, the carrier frequency of IEEE 802.11a standard or IEEE 802.11n standard is 5 GHz and the channel bandwidth thereof is also about 20 MHz. In contrast, an mm-wave uses a carrier frequency of 60 GHz and has a channel bandwidth of about 0.5 to 2.5 GHz. As described above, an mm-wave has significantly larger carrier frequency and channel bandwidth in comparison to the IEEE 802.11 family standards. Thus, by using an mm-wave, a high transmission rate of several Gbps can be obtained, the size of an antenna can be kept to 1.5 mm or less, and a single chip including an antenna can be realized. Also, since attenuation in air is high, interference between devices can also be reduced.
FIG. 2 is a flowchart illustrating a related art process of performing data communication between devices using an mm-wave in a WPAN.
Referring to FIG. 2, in operation 201, a transmitter device and a receiver device perform beam searching. Since directional beams are used in data communication using an mm-wave, various beam paths may be present, wherein these beam paths can establish a link between the transmitter device and the receiver device. Beam searching is a process of searching for various beam paths.
In operation 202, an optimum beam path to be used for establishing a link is selected among the discovered beam paths. For example, a beam path having a largest receiving signal strength in the receiver device may be selected.
In operation 203, the transmitter device and the receiver device establish a link using the selected beam path.
In operation 204, the transmitter device and the receiver device perform data communication using the link. As described above, directional beams are used to perform data communication.
In operation 205, the transmitter and receiver devices judge whether the link for data communication is down. If the link is down, beam searching is performed again to restore the link between the devices using a new beam path.
FIG. 3 is a schematic view for explaining a related art data communication method performed by a WPAN device using an mm-wave.
As illustrated in FIG. 3, a Piconet coordinator (PNC) 310, a device 1 301, a device 2 302, a device 3 303, and a device 4 304 are included in a WPAN.
The device 1 301 desires to transmit data to the device 2 302, and the device 3 303 desires to transmit data to the device 4 304. Accordingly, the device 1 301 and the device 3 303 request the PNC 310 for a wireless resource allocation, and the PNC 310 allocates a channel time allocation period (CTAP) to the device 1 301 and the device 3 303.
The device 1 301 and the device 2 302 perform data communication during a CTAP that is allocated to them. First, the devices 301 and 302 perform beam searching to find a beam path in which to establish a link. The device 1 301 selects a path 1, among the paths found by the beam searching, to perform data communication.
If an obstacle blocks a beam path during data communication using a directional beam such as an mm-wave, it is likely that data communication will be interrupted at the same time as a link goes down. Thus, when an obstacle blocks a path 1, the device 1 301 and the device 2 302 search for beam paths again and find a path 2 and a path 3. Accordingly, the devices 301 and 302 restore the link using an optimum beam path among the found beam paths according to receiving signal strengths.
According to a related art, when the link has gone down because of, for example, an obstacle blocking beam paths in a WPAN in which data communication is performed using directional beams, the devices search for beam paths again, and compare the reception signal intensities of the found beam paths to find an optimum beam path. Thus, a large amount of time and resources are consumed to restore the link. Moreover, when selecting an optimum path among the various beam paths, if another factor besides the receiving signal strength is to be taken into consideration, the above problem becomes more serious and complex.